Purpose :
Inflammation and angiogenesis can have negative effects on the integrity of the blood-retinal barrier in diabetic retinopathy. We have previously shown that in animal models of diabetic retinopathy there are significantly lower levels of sphingosine-1-phosphate (S1P). Also we demonstrated increased tight junction protein expression of the endothelium with purified S1P. We hypothesize that pericyte-derived S1P also plays a role in maintenance of the endothelium in an anti-inflammatory and anti-angiogenic state.

Methods :
Human retinal endothelial cells (HREC) were incubated in high (30.5mM) and normal (5.5mM) glucose for 7 days. Leukocyte adhesion assay on treated HREC was done using fluorescently-labelled U937 macrophages. Changes in ICAM-1 and EphrinB2 mRNA in endothelial cells were examined using TaqMan real time PCR. Additionally, HREC were incubated in media with or without purified S1P for 16 hours, and EphrinB2 and Angiopoietin-2 mRNAs were analyzed. Trans-endothelial resistance changes in HREC treated with S1P were measured by Electric-Cell Substrate Impedance (ECIS).

Results :
Incubation of retinal endothelial cell monolayers in high glucose for 7 days enhanced the adhesion of U937 to the cell surface compared to low glucose incubated cells. This increased adhesion was likely facilitated in part by the increased expression of the cell adhesion molecule ICAM-1 and the anti-angiogenic factor, EphrinB2. In contrast, treatment of HREC with S1P leads to the down regulation of EphrinB2 as well as the pro-inflammatory mediator angiopoietin-2, concomitant with tightening of the endothelial cell barrier.

Conclusions :
We conclude that pericyte-derived S1P can exert anti-angiogenic and anti-inflammatory roles, which may be key for its potential benefit in the maintenance of the blood-retinal barrier in diabetic retinopathy.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.